1. Field of the Invention
Embodiments of the present invention generally relate to supplying a gas or gases to a plasma chamber. More specifically, the invention relates to supporting a gas distribution plate within the chamber.
2. Description of the Related Art
Flat panel displays employ an active matrix of electronic devices, such as insulators, conductors, and thin film transistors (TFT's) to produce flat screens used in a variety of devices such as television monitors, personal digital assistants (PDA's), and computer screens. Generally, these flat panel displays are made of two thin panels of glass, a polymeric material, or other suitable substrate material. Layers of a liquid crystal material or a matrix of metallic contacts, a semiconductor active layer, and a dielectric layer are deposited through sequential steps and sandwiched between the two thin panels which are coupled together to form a large area substrate having at least one flat panel display located thereon. At least one of the panels will include a conductive film that will be coupled to a power supply which will change the orientation of the crystal material and create a patterned display on the screen face.
These processes typically require the large area substrate to undergo a plurality of sequential processing steps that deposit the active matrix material on the substrate. Chemical vapor deposition (CVD) and plasma enhanced chemical vapor deposition (PECVD) are some of the well known processes for this deposition. These known processes require the large area substrate be subjected to temperatures on the order of 300° C. to 400° C. or higher, and maintained in a fixed position relative to a gas distribution plate, or diffuser, during deposition to ensure uniformity in the deposited layers. The diffuser generally defines an area that is equal to or greater than the area of the substrate. If the diffuser is somehow warped during deposition, the process may not produce uniform deposition, which may result in an unusable flat panel display.
Flat panel displays have increased dramatically in size over recent years due to market acceptance of this technology. Previous generation large area substrates had sizes of about 500 mm by 650 mm and have increased in size to about 1800 mm by about 2200 mm or larger. This increase in size has brought an increase in diffuser size so that the substrate may be processed completely. The larger diffuser size has presented new challenges to design a diffuser that will resist sag when exposed to high temperatures during deposition.
The diffuser is generally a plate supported in a spaced-apart relation above the large area substrate with a plurality of openings adapted to disperse a process gas or gases and typically has substantially the same area as the to-be-processed substrate. Diffusers are commonly made of aluminum and are subject to expansion and contraction while enduring the CVD or PECVD processes and are commonly supported around the edges to control spacing between the diffuser and the substrate. However, this edge support scheme does not provide any support for the center portion, which can tend to sag or creep over time, due to the forces of gravity aggravated by high processing temperatures during the CVD or PECVD processes.